5,6-dihalo-2-fluoroalkyl-1h-imidazo(4,5-b)pyrazines

ABSTRACT

COMPOUNDS OF THE FORMULA   2-(F((2N+1)-M)-(C)N(H)M-),5,6-DI(X-)-1H-IMIDAZO(4,5-B)   PYRAZINE   WHEREIN X IS CL, BR OR F (THE SAME IN EACH OCCURENCE), N IS 1 TO 3 AND M IS 0 OR 1, HAVE BEEN FOUND ESPECIALLY USEFUL AS HERBICIDES.

United States Patent Oflice 3,822,261 Patented July 2, 1974 3,822,261 5,6-DIHALO-2-FLUOROALKYL-1H-IMIDAZO(4,5-b) PYRAZINES Yulan C. Tong, Walnut Creek, Califi, assignor to The Dow Chemical Company, Midland, Mich.

No Drawing. Filed Oct. 30, 1972, Ser. No. 301,966 Int. Cl. C0711 51/76 US. Cl. 260-250 R 4 Claims ABSTRACT OF THE DISCLOSURE Compounds of the formula wherein X is Cl, Br or F (the same in each occurrence), n is 1 to 3 and m is or 1, have been found especially useful as herbicides.

BACKGROUND OF THE INVENTION wherein R is H or an alkyl group, are taught as cotton defoliants in US. Pat. 3,401,030. 5,6-dihalo-2-Trifluoromethyl-lH-imidazo(4,5-b)pyridines are taught to have biological activity in US. Pat. 3,561,948.

Substituted imidazopyrazines are also known. For instance, 5,6 dirnethyl 2 R 1H-imidazo(4,5-b) pyrazine, wherein R is H or alkyl, was prepared by Schipper and Day (I. Am. Chem. Soc, 74, 350 (1952)). Day and Muehlman later prepared the 5,6-unsubstituted analog. Both classes were hoped to have some physiological activity. Also reported is 5,6-diphenyl-1H-imidazo(4,5-b) pyrazine (see Chem. Abs., 5], 10533h (1957)).

The structurally closest compound to the instant invention was prepared by Palamidessi and Luini: 5,6-dichloro- 2-methyl-1H-imidazo(4,5-b)pyrazine. (See Farmaco, Ed. Sci, 21 (11), 811 (1966)). No. activity was reported for the compound.

SUMMARY OF THE INVENTION It has now been found that a particular group of imidazopyrazines have surprising biological activity, especially as herbicides. The invention, then, comprises imidazopyrazines of the general formula suitable fiuorinated carboxylic acid or anhydride, or with a fiuorinated acyl halide. Suitable fluorine compounds include trifluoroacetic anhydride, diand tri-fiuoroacetic acid, pentafluoropropionyl chloride and heptafluorobutyryl chloride.

The subject compounds have been found suitable as herbicides, particularly pre-emergent herbicides. Their other biological utilities include their use as insecticides, fungicides and/ or coccidistats.

DETAILED DESCRIPTION OF THE INVENTION More specifically, 5,6-dihalo-2-fluoroalkyl-lH-imidazo (4,5-b)pyrazines may generally be prepared by reacting a 2,3-diamino-5,6-dihalopyrazine with a fiuorinated carboxylic acid, anhydride or acid chloride in an aromatic hydrocarbon (benzene, toluene, xylene, etc.). After the reaction has come to completion (2-24 hours), the reaction mixture is suitably evaporated to dryness under reduced pressure. If, upon examination by analysis, amide functions persist in the product, it may be mixed with diphenyl ether (10 ml. per g.) and the mixture refluxed (260 C.) for about 1 to 2 hours, cooled, diluted with hexane and filtered. A relatively pure product may then be recovered.

The examples below illustrate the preparation of a representative group of the compounds of this invention:

Example 1. 5,6-Dichloro-2-triiluoromethyl-lH-imidazo (4,5 -b pyrazine (a) Nine grams (0.05 mole) of 2,3-diamino-5,6-dichloropyrazine, prepared according to the above-mentioned method of Palamidessi and Luini, and 8 ml. of trifluoroacetic anhydride were mixed in ml. of xylene and heated to boiling under reflux for one hour. To the cooled reaction mixture was then added another 8 ml. of anhydride, and heating continued for another 8 hours. The reaction mix was then evaporated to dryness under reduced pressure, and the residue washed with hexane, filtered and dried. The resulting solid was then mixed with diphenyloxide (10 ml. per g.) and heated to boiling under reflux for one hour, cooled and diluted with hexane. The precipitate was collected and recrystallized from dichloromethane to give 9.5 g. of the titled product, mp. 168-170" C.

Upon analysis, the product was found to have carbon, hydrogen and nitrogen contents of 28.3, 0.7 and 2l.3 weight percents, respectively, as compared with theoretical values of 28.0, 0.4 and 21.8 weight percent calculated for the titled compound.

(b) Alternatively, it has been found that trifluoroacetic acid may also be used in the above reaction, although generally longer (i.e., about 20 hours) reaction times are necessary.

Example 2. 5,6-Dichloro-2-(pentafluoroethyl)-1H- imidazo(4,5-b)pyrazine 4.4 Grams (0.025 mole) of 2,3-diamino-5,6-dichloropyrazine and 50 ml. of xylene were placed in a flask equipped with a Dry Ice-filled condenser, thermometer, magnetic stirrer and gas-inlet tube. 4.5 Grams (0.025 mole) of pentafluoropropionyl chloride was bubbled into the flask, with stirring, while the contents were maintained at about 10-15 C. The reaction mixture was then stirred, at room temperature, for about 4 hours, followed by heating under reflux for about 2 hours. The reaction mix was then evaporated to dryness and residue mixed with 50 ml. of diphenyloxide and heated to 260 C. for 1.5 hours, cooled and precipitated from hexane. 2.6 Grams of the titled product resulted, M.P. 178-9" C.

Upon analysis, the product was found to have carbon, hydrogen and nitrogen contents of 27.7, 0.5 and 17.9 weight percent, respectively, as compared with theoretical values of 27.4, 0.3 and 18.3 weight percent.

3 Example 3. 5,6-Dichloro-2-(n-heptafiuoropropyl)-1H- aminated with 300 g. of concentrated NH OH to give imidazo(4,5-b)pyrazine 24.4 g. of the desired precursor.

7.3 Grams (0.05 mole) of the above pyrazine was then added to 120 ml. of xylene. To this mixture, at room temperature, was added 8 ml. of trifluoroacetic anhydride, the mixture being heated to boiling under reflux for 6 hours. There was recovered 6.7 g. of product with a melting point of ISO-2 C.

Analysis gave carbon, hydrogen and nitrogen contents The titled compound was prepared, as in Example 2 above, from the amino-pyrazine and heptafiuorobutyryl chloride. 3.3 grams of the titled compound with a melting point of 158-60 C. were isolated.

Analysis for carbon, hydrogen and nitrogen content was 27.0, 0.6 and 15.6 weight percent, respectively, as compared with theoretical values of 26.9, 0.3 and 15.7

10 of 32.6, 0.5 and 24.6 weight percents, respectively, as welght percents compared to theoretical values of 32.2, 0.5 and 25.0

Example 4. 5,6-Dichloro-2-difluoromethyl-lH- weight percents.

imidazo(4,5-b)Py Other compounds which can be prepared by the above Using the general method of Example 1b, the pyrgeneral methods Include the followmg:

azine was reacted with difluoroacetic acid in xylene. 4.8 5 tafl 1 4 Grams of the titled product, with an M.P. of 1734 C., lfiuoro (pen Home y mu azo( b) pyrazine resulted- 56-D'b -2- -h tafiuo o l-lH-m'da 0- Carbon, hydrogen and nitrogen analysis indicated g 6P r Propy) l 1 Z weight percents of 30.4, 1.0 and 23.0, respectively, as 5 643m th O compared with theoretical values of 30.2, 0.8 and 23.4 gi uorome y um a2 Weight Pecents- 5,6-Di'bromo-2-l,2,2,2-tetra.fiuoromethyl)-1H-imidazo- Example 5. 5,6-Dibromo-2-trifiuoromethyl-lH- (4,5-b)pyrazine imidazo(4,S-b) pyrazine 5,6-Dichloro-2- (n-hexafluoropropyl) -1H-imidazo- (4,5-b) pyrazine In order to prepare 2,3-diamino-5,6-dibromopyrazine, 56 Difluoro 2 (n hexafluoropropyl) 1H imidaz0(4,5 b)

25 g. (0.063 mole) of tetrabromopyrazine (see U.S. Pat.

3,471,496) was aminated in 200 ml. of concentrated pyrazme' NH OH a 120 C. for 14 hOu S (see the previously cited In order to illustrate the superiority of the compounds article y Palamidessi and 7.2 Grams of the of this invention in regard to their nearest known analog,

desired diamino Compound resulted C.)- i.e., 5,6-dichloro-2-methyl-1H-imidazo(4,5-b)Pyrazine,

To 13.4 grams (0.05 mole) f this diamin th n, Was side-by-side comparisons were run to assess their respecadded 100 ml. of xylene, and the mixture was then give activities as herbicides.

heated to boiling under reflux. To this mixture was slowly An appropriate number of square pots (2%" x 2 /2") added 8 ml. of trifluoroacetic anhydride followed by 20 were filled with #26 soil (85% sand, 10% silt and 5% ml. of xylene. Heating was continued under reflux for clay), aid oil having a, pH of 7. Seeds of the various 24 hours. The reaction mixture was evaporated to dryness plant e ie were then sown at a depth of /2" to under reduced pressure and the residue extracted with Th ot were then placed in a greenhouse and topbenzene followed by sublimation to give 12.7 g. of the tered a necessary.

desired P After the plants had reached a height of about 1 to 2 Q hydrogen and nitrogen analysis indicated inches, an appropriate number were treated with variwelght percents of and p t y, as ous concentrations (i.e., 4000, 2000, 1000, 500, 250, 125, compared with theoretical values of 20.8, 0.3 and 16.2 625, 31,25 and 0 m) of each compound. The treated Weight pefcentsplants were then returned to the greenhouse and sub- Example 5,6 Difluoro 2 trifiuoromethyp1H irrigated daily. Also, they were given IIUII'IGIHS twice imidazouiwwmzine weekly. Two weeks after treatment, they were visually inspected for percent control.

In order to prepare 2,3-d1am1no-5,6-d1fluoropyraZ1n The table below shows the results. A dash indicates 35 mole) of tetFah1f0PyraZ11 1e Was mlXed Wlllh no control in the case of Column (1), i.e., lowest dosage 454 of anhydrous KF and heated bomb f 15 rate at which control was noted; or, in the case of Column hours at The tetrafllloropyl'alme Obtained (2), it indicates no dosage rate at which at least 75% Was collected In traps filled Wlth benzene and P p control was noted. In the case of Column (2), the lowest the combined solution then being saturated with ammonia dosage rate indicated is that at which at least 75% was to produce aminotrifluoropyrazine. This was then further noted; i.e., no extrapolations were made.

Corn Rice Wheat Wild oats Barnyard grass Crabgrass Number Compound 1 2 2 8 1 2 1 2 1 2 1 2 1 2 1 5,6-dichlor0-2-methyl 2,000 1 000 2,000 2.-. 5,6-dlchloro-2-triflu0romethyl 250 2,000 62.5 250 500 2,000 31.25 31.25 62.5 31.25 62.5 3 5,6-dichloro-2-pentafluoroethyl-- 500 000 62.5 1,000 250 2,000 62.5 250 62 5 250 62.5 125 4..- 5,6-dichloro-2-heptafluoropropyl. 2,000 250 4,000 1,000 4,000 500 1,000 125 500 62.5 250 5... 5,6-d1chloro-2-difluoromethyl 1,000 4,000 31.25 125 250 1,000 31.25 125 62.5 125 250 1,000 6 5,6-dibromo-2-trifluoromethyl. 500 4,000 125 2,000 1,000 4,000 125 500 31.25 125 62.5 250 Annual Johnson German Velvet morning N I grass Sorghum mullet lea! glory Rape Soybean Cotton Pigweed Bindweed 0.0 Compound 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 Prior art compound. 1 Lowest dosage at which control was observed. 8 Lowest dosage at which at least 75% was observed.

The various analogs of the instant invention have also been found biologically useful as follows: 5,6-dichloro-2- pentafluoroethyland 5,6 dibromo 2 difiuoromethyl-, 100% control of houseflies at 500 p.p.rn.; 5,6-dichloro-2- trifluoromethyl-, 5,6-dich1oro-2-difiuoromethyland 5,6- dibrorno-2-trifiuoromethyl-, 100% control of houseflies at 250 p.p.rn.; 5,6-difluoro-2-trifluoromethyl, 100% control of round worms (human) at 300 p.p.rn.; and 5,6-dibromo and difiuoro-2-trifluoromethyl-, 100% control of wheat leaf rust fungus at 25 p.p.rn. Also, the following analogs, at 100 to 500 p.p.rn., gave 50 to 100% control of some common microorganism (e.g., Bacillus subtilis, Staphyl. ococcus aureus, Escherichia coli, Salmonella typhosa, Mycobacterium phlei and Trichophton mentagrophytes): 5,6-dichlorodibromo and difluoro-2-trifluoromethyl; 5,6- dichloro and dibromo-Z-difluoromethyl; and 5,6-dichloro- Z-pentafluoroethyl.

Preferred species of the instant invention include 5,6- dichloro, dibromo or difluoro-Z-trifiuoromethyl-lH-imidazo (4,5-b) pyrazine; 5,6 dichloro-2-difluoromethyl- 1H- imidazo(4,5- b)pyrazine; and 5,6-dich1oro 2 pentafiuoromethyl-1H-imidazo(4,5-b)pyrazine.

6 I claim: 1. Imidazopyrazines of the formula wherein X is Cl, Br or F, the same in each occurrence; n is 1 to 3; andmisOor 1.

2. The compound of Claim 1 wherein n is 1 and m is 0.

3. The compound of Claim 1 wherein X is Cl, n is 1 and m is 1.

4. The compound of Claim 1 wherein X is Cl, n is 2 and m is 0.

References Cited Palamidessi et -al.C.A. 66, 37886g (1967).

DONALD G. DAUS, Primary Examiner R. V. RUSH, Assistant Examiner US. Cl. X.R. 71-92; 260-999 

